In the field of toners for electrophotography, with the progress of electrophotographic systems, it has been demanded to develop toners adaptable for high image quality and high copying or printing speed.
To meet a high image quality, there are known processes for producing toners having a narrow particle size distribution and a small particle size by an aggregating and coalescing method (emulsification-aggregation method or aggregation-coalescence method) in which fine resin particles, etc., are aggregated and coalesced together in an aqueous medium.
For example, Patent Literature 1 discloses a process for producing a developer which includes a step of adding an aggregating agent to a dispersion containing a binder resin and colorant-containing fine particles to aggregate the fine particles with the binder resin, and a step of coalescing the resulting aggregated particles together to form toner particles, for the purpose of attaining a high image quality and producing a developer having a good particle size distribution. In the production process, a pH value of the dispersion before adding the aggregating agent thereto, a pH value of the dispersion after adding the aggregating agent thereto and a pH value of the dispersion after coalescing the particles are controlled to satisfy a specific relationship with each other.
On the other hand, Patent Literature 2 discloses a process for producing a toner for development of electrostatic images in which an emulsion prepared by emulsifying a shell-forming resin in an aqueous medium containing 25 to 35% by mass of methyl ethyl ketone is added twice or more to a dispersion containing colored resin fine particles, and then an electrolyte aqueous solution is added to the resulting dispersion to form particles having a core/shell structure, for the purpose of producing a toner for development of electrostatic images which contains a less amount of coarse particles, is free from separation of the shell and aggregation of the toner during storage, and has such a core/shell structure as is capable of satisfying both a good low-temperature fusing property and a good heat-resistant storage stability.    Patent Literature 1: JP 2009-122674A    Patent Literature 2: JP 2008-20478A